Inkjet printers can be used for single or multiple color printing of a printing substrate, e.g. a single sheet or a band-shaped recording medium made of different materials. The assembly of these inkjet printers is known, for example, from EP 0 788 882 B1. Inkjet printers which function according to the Drop on Demand (DoD) principle exhibit one print head or numerous print heads having jets comprising ink channels, the activators of which, controlled by a printer control, propel ink droplets toward a printing substrate in order to apply printer dots thereto to create a print image. The activators can generate print drops thermally (bubble jet) or by piezoelectric means.
In order to replace the ink used by a print head in printing, it is known from DE 33 16 970 C2 to dispose a supply chamber filled with ink next to the print head. A main container for ink is supplied for filling the supply chamber with ink, and which can be coupled to the supply chamber as needed in order to supply ink to the supply chamber. In order to prevent an overflow of ink in the supply chamber, a separating wall to an overflow chamber is disposed in the supply chamber. If the ink in the supply chamber overruns the separating wall, ink flows over the separating wall into the overflow chamber. From there, the ink can be returned to the main container, for example, when the supply chamber is coupled to the main container. The supplying of ink into the supply chamber and the removal of ink from the overflow chamber is obtained in each case by means of a pump. The height of the separating wall is selected such that the level of ink in the supply chamber exhibits a state such that the ink supply pressure at the jets of the print head is maintained at a constant level.
A multi-color printer is known from DE 36 23 251 A1with which successive print images of different colors can be printed using the same developer station. The dyes can be supplied to the developer station from a tank, which contains the respective dyes. The excess dyes can be returned to the dye tank via a rotatably mounted jet. When a color change is to be carried out, the developer station must be cleaned with a cleaning fluid between changes. Overflow holes are provided in the dye tanks, each of which is connected to an overflow tank.
With the known inkjet printer according to DE 33 16 970 C2, an intermediate tank (called a supply chamber) is thus provided, which supplies the print head with ink. The ink in the intermediate tank is subjected to pressure thereby, e.g. a hydrostatic pressure, such that the ink is supplied to the jets of the print head.
With lower print loads, not all of the jets of a print head are activated during a printing process, and numerous jets are inactive (printing breaks), with the result that the ink in the ink channel of those jets remains stationary. Due to the effect of evaporation from the jet opening, there is the risk that the viscosity of the ink then changes. This results in the ink in the ink channel no longer being able to flow in the optimal manner, and thus exit the jet. In extreme cases, the ink dries in the ink channel, and clogs the ink channel, such that a printing with this jet is no longer possible.
A drying up of the ink in the jets of a print head during the printing breaks presents a problem which can be prevented in that, within a given cycle, for example, a flushing medium, e.g. ink or cleaning fluid, can be flushed through the jets. This flushing cycle can, for example, be adjusted in accordance with the printing load.
The flushing process can be carried out using the ink in the intermediate tank, wherein the pressure applied to the ink in the intermediate tank can be generated using a pressure source, which is connected to the intermediate tank by means of a pressure line. When a printer exhibits numerous print heads, e.g. as in the case with color printing, an intermediate tank can be allocated to each print head. By this means, the necessary pressure can be generated in all of the intermediate tanks with a pressure source, wherein the pressure lines lead to the pressure source from all of the intermediate tanks. If, in this case, one of the intermediate tanks overflows, e.g. because too much ink was sent to the intermediate tank, there is the risk that ink from this intermediate tank will end up being sent, via the pressure lines, to the other intermediate tanks and print heads. This is particularly the case when the pressure source is shut off during the printing operation, and only the hydrostatic pressure provided for the printing is present in the intermediate tank.